The Winter Workout

"Twelve to 16 hours of hiking and 5,000 vertical feet of climbing is a long day for anyone," says Darsie Culbeck, an 18-year high-altitude trip leader and director of Alaska Mountain Guides. But that's exactly what many hikers try to do–straight off the couch–when peakbagging season starts. Train wisely in winter, advises Culbeck, or risk injury when the weather warms. Follow his tips for getting mountain-fit in the gym:

Lungs

"At the top of a mountain, you've got to be able to process oxygen," says Culbeck. Aim to increase stamina and lung power with three weekly stair-stepper or treadmill workouts at 80 percent of your maximum heart rate (subtract your age from 220 to find your max). Begin with 20-minute sessions, adding a few minutes each week as your aerobic capacity improves. "Increase the length to 45 minutes within two months, and you're moving toward expert fitness," Culbeck says.

Legs

Culbeck's clients need the quad and hamstring strength to haul up to 60 pounds on extended excursions. He recommends boosting leg power by wearing a pack for one of your weekly stair-stepper sessions: "Start with 15 pounds and build up to what you'll be carrying on an upcoming trip." The workout he suggests to his Denali-bound hikers: a five-minute warm-up, 15 minutes at a moderate pace with the weighted pack, 15 minutes at a fast pace without the pack, and a five- to 10-minute cool down. Big spring trip planned? Increase frequency to twice weekly the month before you leave.

Mind

"Making sure your workout actually happens is the most important thing," says Culbeck–the endurance you build now can make or break your next big trip. Stay motivated to keep training (and beat gym fatigue) by supplementing indoor workouts with one multi-hour hike, ski, or snowshoe outing per week.